Electric Charges and Fields — Physics STD 12 Science — Question

Light with an energy flux of 20W/cm² falls on a non-reflecting surface at normal incidence. If the surface has an area of 30cm². the total momentum delivered (for complete absorption) during 30 minutes is:

A parallel-plate capacitor is connected to a battery. A metal sheet of negligible thickness is placed between the plates. The sheet remains parallel to the plates of the capacitor:

Assertion   :   Photoelectric effect demonstrates the wave nature of light.

Reason       : The number of photoelectrons is proportional to the frequency of light.

(a) If both assertion and reason are true and the reason is the correct explanation of the assertion.

(b) If both assertion and reason are true but reason is not the correct explanation of the assertion.

(c) If assertion is true but reason is false.

(d) If the assertion and reason both are false.

A rod AB moves with a uniform velocity v in a uniform magnetic field as shown in figure.

1. The rod becomes electrically charged.
2. The end A becomes positively charged.
3. The end B becomes positively charged.
4. The rod becomes hot because of Joule heating.

The energy stored in a charged capacitor is:

On decreasing the distance between the plates of a parallel plate capacitor, its capacitance:

A Young's double slit experiment uses a monochromatic source. The shape of the interference fringes formed on a screen is

(a) Straight line

(b) Parabola

(c) Hyperbola

(d) Circle

Two sound waves move in the same direction in the same medium. The pressure amplitudes of the waves are equal but the wavelength of the first wave is double the second. Let the average power transmitted across a cross-section by the first wave be P₁ and that by the 1 second wave be P₂. Then,

1. P₁ = P₂
2. P₁ = 4P₂
3. P₂ = 2P₁
4. P₂ = 4P₁

In a p-n junction with open ends: